Conventionally, in manufacture of a rotor of a motor used for an automobile or a home electric appliance, a plurality of magnet insertion holes are provided in an annular core body, where the number of the holes corresponds to the number of magnetic poles, and unmagnetized permanent magnets are sealed in the holes with resin. In this technique, while the core body with the permanent magnets inside the magnet insertion holes is held between an upper die and a lower die, a thermosetting resin is injected into the holes via runners from resin reservoir pots provided in the upper die or the lower die.
However, after the resin-sealing process, a laminated core (i.e., the core body with the magnets resin-sealed therein) needs to be detached from between the upper die and the lower die, and a surface of the laminated core needs to be cleaned by removing the cured resin adhering around gates of the magnet insertion holes, which results in poor workability. In light of this, for example, Patent Literature 1 discloses a technique of placing a dummy plate between a core body with permanent magnets inserted therein and an upper die or a lower die having resin reservoir pots, sealing the magnets with resin, and thereafter removing residual resin together with the dummy plate from a laminated core.